/*
 * Copyright (c) 2011-2015 Pivotal Software Inc, All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.camunda.bpm.extension.reactor.projectreactor.reactivestreams;

import org.reactivestreams.Subscription;

import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;

/**
 * A {@link Subscription} with a typed stateful context. Some request utils are also provided to read pending demand and
 * request relatively to it.
 *
 * @author Stephane Maldini
 * @since 2.0.2
 */
public class SubscriptionWithContext<C> implements Subscription {

  private volatile long pending = 0;
  protected static final AtomicLongFieldUpdater<SubscriptionWithContext> PENDING_UPDATER = AtomicLongFieldUpdater
    .newUpdater(SubscriptionWithContext.class, "pending");

  private volatile int terminated = 0;
  protected static final AtomicIntegerFieldUpdater<SubscriptionWithContext> TERMINATED_UPDATER = AtomicIntegerFieldUpdater
    .newUpdater(SubscriptionWithContext.class, "terminated");


  protected final C context;
  protected final Subscription subscription;

  /**
   * Attach a given arbitrary context (stateful information) to a {@link Subscription}, all Subscription methods
   * will delegate properly.
   *
   * @param subscription the delegate subscription to invoke on request/cancel
   * @param context      the contextual state of any type to bind for later use
   * @param <C>          Type of attached stateful context
   * @return a new Subscription with context information
   */
  public static <C> SubscriptionWithContext<C> create(Subscription subscription, C context) {
    return new SubscriptionWithContext<>(context, subscription);
  }

  protected SubscriptionWithContext(C context, Subscription subscription) {
    this.context = context;
    this.subscription = subscription;
  }

  /**
   * The stateful context C
   *
   * @return the bound context
   */
  public C context() {
    return context;
  }

  @Override
  public void request(long n) {
    subscription.request(n);
  }

  @Override
  public void cancel() {
    if (TERMINATED_UPDATER.compareAndSet(this, 0, 1)) {
      subscription.cancel();
    }
  }

  public boolean isCancelled() {
    return terminated == 1;
  }

}
